Take the following sentence:

The train was frequently loud and late.

If I want to say that the train was both frequently loud and frequently late, would the above sentence be accurate in conveying my meaning? Or should it be: "The train was frequently loud and frequently late." I wonder if the first sentence actually means the train was frequently loud, and also late (but not necessarily frequently).

Thanks in advance.
Once you have "The train was frequently ...", you've set up a sentence talking about something that happens habitually. It's hard to see how anyone would be able to interpret the sentence as a whole as talking about something habitual with regard to loudness, but a one-time event with regard to lateness.

Even separating the two results in something anomalous:

The train was frequently loud, and it was late.

What could that mean? Or, to put it differently, why would a speaker combine a fact about the habitual loudness of the train with the fact that it was late on this occasion?

The only interpretation that makes sense is to take frequently as applying to both adjectives loud and late.

Each sentence has its own logic, however, so there may be other cases where the adverb applies only to one adjective.

Students: We have free audio pronunciation exercises.
The train was frequently loud and late.

To resove all ambiguity, write the sentence as follows. The train was frequently both loud and late.
So I guess examining each individual writing situation is more important than following hard and fast rules..

much appreciated, btw. Emotion: smile